The focus of the research to be pursued in the next three-year period will be an attempt to establish the rudiments of the biochemical genetics fo polyether antiobiotic biosynthesis by Streptomyces spp. We will study the biosynthesis of three polyether antibiotics: lasalocid A (S. lasaliensis), monensin A (S. cinnamonensis), and salinomycin (S. albus) by biochemical, mutational, and gene cloning experiments. In the comtinuation of our lasalocid A study, we will develop a collection of non-producing (Las-) mutants and identify compunds accumulated by them in fermentation broth. The results of cosynthesis and biotransformation experiments will be used to obtain a biochemical complementation map of the lasalocid A biosynthetic pathway. The gene for lasalocid A self-resistance will be cloned from S. lasaliensis. Then two approached to cloning las genes will be investigated using the Las- mutants and the las resistance gene. The las genes cloned will be mapped by restriction endonuclease digestion, and attempts will be made to map las genes genetically. Mutational cloning of las genes will be used to define the number and size of the transcriptional units of the las gene. The results of this work will be interpreted in relation to a hypothesis for the genetic organization of the putative polyether synthetase (PES) multifunctional protein system. A study of the regulation of lasalocid A production will be initiated by focusing on the role of valine catabolism in the process. Analogous studies will be initiated with the Streptomyces producing monesin A and salinomycin as part of our long-range research goal to create hybrid polyether antibiotics by artificial translocation of DNA encoding the PEs gene.